Controls for a Crab Drive

[Astronouth7303]

I'm trying to build a mini-bot using the system I described earlier. I will use servos for steering and motors for drive.

The controls will be 4 sticks. Mapping is vector/speed. How? check "Angle from X,Y" in the Programming forum.

[Rob Ciavaglia]

We have experimented with a few different methods and I would have to say that the best method that we found is to use pots to align the wheels in the direction you wish to travel. One year we limited the robot to find 5 different angles by using two foot pedals and the trigger on the joystick. The programming for this was rather simple.

We calibrated the pot so that when nothing was depressed, we traveled forward. For this example, I will say the value was 130. When we pressed the right foot pedal, we told the pot to change to 190. That gave us a 60 degree angle to right from the front. If we held the trigger and pressed the right foot pedal, we set the pot to 220 or 90 degrees to the right. By pressing the left foot pedal by itself, we commanded the pot to 70 and by the pressing the trigger with the left pedal we commanded the pot to 40.

The same was tried with using a pot and knob on the control board. Whatever we set the knob to on the control board, the pot on the robot would pivot the wheels to a corresponding setting. With the wheels pivoted, we in essence altered the front of the robot.

Both methods required very little programming. However, since we used the window motor and a 1/4" chain, we had several issues mechanically.

Robert

[Matt Reiland]

In 2001 when we did the swerve, we used one joystick for everything, in normal more the robot drove around like a non-swerve bot. When you held in the trigger it was in swerve and the crab modules followed the joystick vector. However with some experimenting the best I can come up with is something like a MS sidewinder force feedback that had the ability to twist the joystick for a third axis. This way X and Y would be the swerve vector then to rotate, twist the joystick. It seems to be VERY natural when you get used to it.

My 2 coppers

[I.Green]

Does anyone have a picture or something of crab drive system?

[Joe Johnson]

Originally Posted by I.Green

Does anyone have a picture or something of crab drive system?

Here is one of the Grand Dads of Swerve Drive: CD6






There are many more pictures of CD6 HERE

As to control, I like this method:

2 Joysticks

Y position is aways Forward / Back Tank style drive (fight stick in front of the left implies "twist CCW")

average of X positions define what direction is "FORWARD" (both joysticks to the right - "to the robot's right is FOWARD" both joysticks to the left - "to the robot's left is FORWARD" One Joystick left - "45 Deg. to Left is FORWARD" )

It is makes sense to the driver once they drive for a few minutes: Side to side controls the direction of FORWARD with respect to the robot other than that it behaves like a simple tank drive.

Joe J.

P.S. If my typing is a bit messy it is probably due to the tears in my eyes at having seen my old friend CD6 again. Ah yes, we had such fun together...

[Josh Hambright]

For the year 461 did crab drive, we had a 2 stick setup. 1 Stick was for direction of the robot, and one was simply a throttle. However, we had a button that could switch from crab drive to one stick tank control, with trottle on the other stick easily for situations when that was advantagous.

[AIBob]

what my team did two years ago, when we had crab drive is have it so that you had the normal drive and then pushed the trigger, then you went to the other axis

[tkwetzel]

Originally Posted by Matt Reiland

...the best I can come up with is something like a MS sidewinder force feedback that had the ability to twist the joystick for a third axis. This way X and Y would be the swerve vector then to rotate, twist the joystick. It seems to be VERY natural when you get used to it.

That is exactly what I would do. It relates to the robot movement better than anything else you could do with out actually moving a model of the robot. The only problem, which is apparent in any swerve or omni drive, is that you need to know which side of your robot is the front which can easily be marked or identified somehow on most robots.